14557 Views 6 Replies Latest reply: Jun 16, 2009 7:43 AM by MattHagen
Try the general restore troubleshooting tips in this article: http://support.apple.com/kb/TS1275
Make sure the iPhone is directly connected to a high-speed USB2 port on the Mac, using the cable that came with it.
CANT RESTORE IPHONE ERROR 21 wrote:
hi. When i try to restore my iPhone, it says "Cannot restore unknown error 21"
Have you tried restoring the iphone in DFU Mode?
Step 1. Turn off your iPhone.
Step 2. Hold down the power and home button.
Step 3. When you see the Apple logo, release the power button but continue holding the home button down.
Step 4. Open iTunes and wait for it to tell you that its in restore mode.
Step 1. Connect iphone to USB then listen to the sound when it connect and disconnect.
Step 2. Hold the home and power buttons until hear the disconnect sound then release power button.
Step 3. Wait until you hear another sound then release home button.
Funny - I have exactly the same problem.
I was having problems with the earphones and tried to use the "RESTORE" button on iTunes (8.2) to fix it. It hung while contacting Apple, and now the phone is stuck in restore mode but won't complete the restore process, giving an Error 21 each time.
DFU mode doesn't work, and neither did the Geniuses. Their advice: buy a new one.